Device for high voltage applications

ABSTRACT

A device includes a buried oxide layer disposed on a substrate, a first region disposed on the buried oxide layer and a first ring region disposed in the first region. The first ring region includes a portion of a guardring. The device further includes a first terminal region disposed in the first ring region, a second ring region disposed in the first region and a second terminal region disposed in the second ring region. The first terminal region is connected to an anode and the second terminal region is connected to a cathode. The first region has a graded doping concentration. The first region, the second ring region and the second terminal region have a first conductivity type, and the first ring region and the first terminal region have a second conductivity type. The first conductivity type is different from the second conductivity type.

TECHNICAL FIELD

The present disclosure relates generally to a device for high voltageapplications, in particular, a Schottky diode device.

BACKGROUND

The Schottky diode is a semiconductor diode formed by the junction of asemiconductor with a metal.

There is a need to enhance the breakdown voltages of Schottky diodes forhigh voltage applications.

SUMMARY

According to an aspect of the present disclosure, there is provided adevice including: a buried oxide layer disposed on a substrate; a firstregion disposed on the buried oxide layer; a first ring region disposedin the first region, the first ring region comprising a portion of aguardring; a first terminal region disposed in the first ring region,the first terminal region being connected to an anode; a second ringregion disposed in the first region; a second terminal region disposedin the second ring region, the second terminal region being connected toa cathode; wherein the first region has a graded doping concentration;wherein the first region, the second ring region, and the secondterminal region have a first conductivity type; wherein the first ringregion and the first terminal region have a second conductivity type;and wherein the first conductivity type is different from the secondconductivity type.

According to an aspect of the present disclosure, there is provided amethod for manufacturing a device, including: providing a buried oxidelayer on a substrate; providing a first region on the buried oxidelayer; providing a first ring region and a second ring region in thefirst region; and providing a first terminal region disposed in thefirst ring region and a second terminal region in the second ringregion, the first terminal region being connected to an anode and thesecond terminal region being connected to a cathode, wherein providingthe first region comprises: using a photoresist mask when doping thefirst region; and annealing the first region after doping the firstregion; wherein the photoresist mask has a plurality of concentricrings; and wherein the first region, the second ring region, and thesecond terminal region have a first conductivity type; wherein the firstring region and the first terminal region have a second conductivitytype; and wherein the first conductivity type is different from thesecond conductivity type.

These and other advantages and features of the embodiments hereindisclosed, will become apparent through reference to the followingdescription and the accompanying drawings. Furthermore, it is to beunderstood that the features of the various embodiments described hereinare not mutually exclusive and can exist in various combinations andpermutations.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, like reference characters generally refer to the samefeatures throughout the different drawings. Also, the drawings are notnecessarily to scale, emphasis instead generally being placed uponillustrating the principles of the disclosure. Embodiments of thedisclosure will now be illustrated for the sake of example only withreference to the following drawings, in which:

FIGS. 1A and 1B show top views of devices for high voltage applicationsaccording to various embodiments of the present disclosure;

FIG. 2 shows a cross-sectional view of the devices of FIGS. 1A and 1Balong the A-A′ line;

FIG. 3 shows a partial equivalent circuit of the device of FIG. 2 ;

FIG. 4 shows simulated total current densities for the device of FIG. 2in technology computer aided design (TCAD);

FIG. 5 shows a cross-sectional view of the device of FIG. 1B along theB-B′ line;

FIGS. 6A and 6B show the forwarding voltages and breakdown voltages ofthe device of FIG. 1(A), respectively;

FIGS. 7A and 7B show the forwarding voltages and breakdown voltages ofthe device of FIG. 1B, respectively;

FIGS. 8A to 8D show simplified cross-sectional views that illustrate amethod for fabricating the device of FIG. 2 ;

FIG. 9 shows a cross-sectional view of a device for high voltageapplications according to various embodiments of the present disclosure;

FIGS. 10A to 10D show simplified cross-sectional views that illustrate amethod for fabricating the device of FIG. 9 ; and

FIG. 11 shows the doping concentration and electrical fieldcharacteristics of a device for high voltage applications according tovarious embodiments of the present disclosure.

DETAILED DESCRIPTION

Embodiments generally relate to semiconductor devices. Moreparticularly, some embodiments relate to Schottky diode devices.

Aspects of the present disclosure and certain features, advantages, anddetails thereof, are explained more fully below with reference to thenon-limiting examples illustrated in the accompanying drawings.Descriptions of well-known materials, fabrication tools, processingtechniques, etc., are omitted so as not to unnecessarily obscure thedisclosure in detail. It should be understood, however, that thedetailed description and the specific examples, while indicating aspectsof the disclosure, are given by way of illustration only, and are not byway of limitation. Various substitutions, modifications, additions,and/or arrangements, within the spirit and/or scope of the underlyinginventive concepts will be apparent to those skilled in the art fromthis disclosure.

The non-limiting embodiments described below in context of the devicesare analogously valid for the respective methods, and vice versa.Furthermore, it will be understood that the embodiments described belowmay be combined; for example, a part of one embodiment may be combinedwith a part of another embodiment.

Approximating language, as used herein throughout the specification andclaims, may be applied to modify any quantitative representation thatcould permissibly vary without resulting in a change in the basicfunction to which it is related. Accordingly, a value modified by a termor terms, such as “about,” is not limited to the precise valuespecified. In some instances, the approximating language may correspondto the precision of an instrument for measuring the value. The word “or”is intended to include “and” unless the context clearly indicatesotherwise.

The terminology used herein is for the purpose of describing particularexamples only and is not intended to be limiting of the disclosure. Asused herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprise” (andany form of comprise, such as “comprises” and “comprising”), “have” (andany form of have, such as “has” and “having”), “include (and any form ofinclude, such as “includes” and “including”), and “contain” (and anyform of contain, such as “contains” and “containing”) are open-endedlinking verbs. As a result, a method or device that “comprises,” “has,”“includes” or “contains” one or more steps or elements possesses thoseone or more steps or elements, but is not limited to possessing onlythose one or more steps or elements. Likewise, a step of a method or anelement of a device that “comprises,” “has,” “includes” or “contains”one or more features possesses those one or more features, but is notlimited to possessing only those one or more features. Furthermore, adevice or structure that is configured in a certain way is configured inat least that way, but may also be configured in ways that are notlisted.

It should be understood that the terms “on”, “over”, “top”, “bottom”,“down”, “side”, “back”, “left”, “right”, “front”, “lateral”, “vertical”,“side”, “up”, “down” etc., when used in the following description areused for convenience and to aid understanding of relative positions ordirections, and not intended to limit the orientation of any device, orstructure or any part of any device or structure. Similarly, the term“in” as used herein is not intended to limit a thing to be fullyenclosed by something else. Further, the term “width” is intended tomean a length extending in the lateral direction with reference to therelevant drawings; the term “depth” is intended to mean a lengthextending in the vertical direction with reference to the relevantdrawings.

As used herein, the term “connected,” when used to refer to two physicalelements, means a direct connection between the two physical elements.The term “coupled,” however, can mean a direct connection or aconnection through one or more intermediary elements. The term “coupled”(or “connected”) herein may be understood as electrically coupled or asmechanically coupled, for example attached or fixed, or just in contactwithout any fixation, and it will be understood that both directcoupling or indirect coupling (in other words: coupling without directcontact) may be provided.

According to various non-limiting embodiments, a device may include: aburied oxide layer disposed on a substrate; a first region disposed onthe buried oxide layer; a first ring region disposed in the firstregion, the first ring region comprising a portion of a guardring; afirst terminal region disposed in the first ring region, the firstterminal region being connected to an anode; a second ring regiondisposed in the first region; a second terminal region disposed in thesecond ring region, the second terminal region being connected to acathode; wherein the first region has a graded doping concentration;wherein the first region, the second ring region, and the secondterminal region have a first conductivity type; wherein the first ringregion and the first terminal region have a second conductivity type;and wherein the first conductivity type is different from the secondconductivity type.

According to various non-limiting embodiments, the first region may havea rounded shape and the doping concentration of the first region mayincrease in a radial direction from a center of the first region to aperimeter of the first region.

According to various non-limiting embodiments, the first region maycomprise a plurality of concentric ring portions that has been annealed,and the doping concentration of the first region may increase in aradial direction from a center ring portion to a perimeter ring portion.

According to various non-limiting embodiments, the plurality of theconcentric ring portions may be located concentric with the first ringregion and the second ring region.

According to various non-limiting embodiments, the first region mayfurther comprise a plurality of substrate portions in between theplurality of concentric ring portions.

According to various non-limiting embodiments, the device may furthercomprise a first isolation region disposed in the first region, an inneredge of the first isolation region being in direct contact with thefirst ring region, an outer edge end of the first isolation region beingin contact with the second terminal region and the second ring region.

According to various non-limiting embodiments, the device may furthercomprise a first field poly plate disposed over the first isolationregion, the first field poly plate being connected to the anode.

According to various non-limiting embodiments, the first field polyplate may be disconnected with the first and second terminal regions.

According to various non-limiting embodiments, the first ring region maycomprise a discontinuous guardring portion.

According to various non-limiting embodiments, the discontinuousguardring portion may comprise a plurality of guardring portions spacedapart by a plurality of gap portions.

According to various non-limiting embodiments, the plurality ofguardring portions may have a length larger than a length of theplurality of gap portions.

According to various non-limiting embodiments, the device may furthercomprise a second isolation region at least partially disposed in thefirst region, the second isolation region extends laterally from thesecond ring region, a first end of the second isolation region being indirect contact with the second terminal region and the second region;and a deep isolation region in direct contact with the second isolationregion and extending to the buried oxide layer.

According to various non-limiting embodiments, the device may furthercomprise a silicide layer disposed over the first terminal region, thefirst ring region and the first region, wherein the first terminalregion is connected to the anode through the silicide layer.

According to various non-limiting embodiments, the device may furthercomprise a second region; a third region disposed in the second region,the third region being connected to a drain and in direct contact withthe buried oxide layer; a third ring region disposed in the secondregion, the third ring region being connected to a source and in directcontact with the buried oxide layer; and a third isolation regiondisposed in the second region extending between the third region and thethird ring region, the third isolation region being in direct contactwith the third region, wherein a second end of the second isolationregion is in direct contact with the third ring region; wherein the deepisolation region is located between the second ring region and the thirdring region; wherein the second region and the third region have a firstconductivity type; and wherein the third ring region has a secondconductivity type.

According to various non-limiting embodiments, the device may furthercomprise a second field poly plate disposed over the third isolationregion, the second region and the third ring region.

According to various non-limiting embodiments, the first, secondterminal regions may comprise a first, second terminal ring regions.

According to various non-limiting embodiments, a doping concentration ofthe second ring region may be lower than a doping concentration of thefirst region.

According to various non-limiting embodiments, the first region may be adrift region.

According to various non-limiting embodiments, a method formanufacturing a device may include: providing a buried oxide layer on asubstrate; providing a first region on the buried oxide layer; providinga first ring region and a second ring region in the first region; andproviding a first terminal region disposed in the first ring region anda second terminal region in the second ring region, the first terminalregion being connected to an anode and the second terminal region beingconnected to a cathode, wherein providing the first region comprises:using a photoresist mask when doping the first region; and annealing thefirst region after doping the first region; wherein the photoresist maskhas a plurality of concentric rings; and wherein the first region, thesecond ring region, and the second terminal region have a firstconductivity type; wherein the first ring region and the first terminalregion have a second conductivity type; and wherein the firstconductivity type is different from the second conductivity type.

FIG. 1A shows a top view of a device 100 a and FIG. 1B shows a top viewof a device 100 b for high voltage applications according to variousembodiments of the present disclosure. FIG. 2 shows a cross-sectionalview of the device 100 a and the device 100 b (hereafter “the device100”) along the A-A′ line. The device 100 will be described in detailsbelow with reference to FIGS. 1A and 1B and FIG. 2 .

The device 100 may include a buried oxide layer 109 disposed on asubstrate 108. The substrate 108 may be an Epitaxial (EPI) orSilicon-on-Insulator (SOI) substrate for high reverse breakdownvoltages. The buried oxide layer 109 may isolate any regions disposedthereabove as introduced later from the substrate 108. The device 100may further include a first region 110 disposed on the buried oxidelayer 109, and a first ring region 120 (shown as 120 a in FIG. 1A and120 b in FIG. 1B) disposed in the first region 110, the first ringregion 120 may be a well region. The first ring region 120 may include aportion of a guardring that is lightly doped to prevent leakage currentunder reverse state. Referring to FIG. 2 , the first ring region 120, ina cross-sectional view, may include a first portion 121 and a secondportion 122 of the first ring region 120.

The device 100 may further include a first terminal region 130 disposedin the first ring region 120, and the first terminal region 130 may beconnected to an anode 101. The first terminal region 130 may also be aring-shaped region. The first terminal region 130, in a cross-sectionalview, may include a first portion 131 and a second portion 132 of thefirst terminal region 130 disposed in the first portion 121 and thesecond portion 122 of the first ring region 120, respectively.

The device 100 may further include a second ring region 140 at leastpartially disposed in the first region 110 and a second terminal region150 disposed in the second ring region 140, and the second terminalregion 150 may be connected to a cathode 102. The second ring region 140may be a middle voltage well region that is low doped to obtain highreverse breakdown voltage in cathode area. Referring to FIG. 2 , thesecond ring region 140, in a cross-sectional view, may include a firstportion 141 and a second portion 142 of the second ring region 140. Thesecond terminal region 150 may also be a ring-shaped region. The secondterminal region 150, in a cross-sectional view, may include a firstportion 151 and a second portion 152 of the second terminal region 150disposed in the first portion 141 and the second portion 142 of thesecond ring region 140, respectively.

The second ring region 140 may surround the first ring region 120. Thesecond ring region 140 may be spaced away from the first ring region120. Additionally, the second ring region 140 may be concentric with thefirst ring region 120. Furthermore, the first ring region 120 may bedisposed near a center of the first region 110 and the second ringregion 140 may be disposed at or near a perimeter of the first region110.

The first region 110, the second ring region 140, and the secondterminal region 150 may have a first conductivity type, and thesubstrate 108, the first ring region 120 and the first terminal region130 may have a second conductivity type, wherein the first conductivitytype is different from the second conductivity type. In someembodiments, the first conductivity type may be n-type and the secondconductivity type may be p-type.

The first region 110 may be a drift region and have a graded dopingconcentration. That is, the doping concentration of the first region 110may vary across the first region 110 rather than being uniformlydistributed throughout the first region 110. The first region 110 mayhave a rounded shape, for example a circle shape or an oval shape. Thedoping concentration of the first region 110 may increase in a radialdirection from a center area of the first region 110 to a perimeter areaof the first region 110. Said differently, the doping concentration ofthe first region 110 may be lowest at the center area of the first ringregion 120 and may gradually increase in a direction moving towards thesecond ring region 140. To provide the graded doping concentration,different portions of the first region 110 may be implanted to have thedoping concentration increase in a step-wise manner. That is, the firstregion 110 may include a plurality of concentric ring (or annulus)portions 111 to 116, and the doping concentration of the first region110 may increase in a radial direction from a center ring portion 111 toa perimeter ring portion 116, as shown in FIGS. 1A and 1B. It should beappreciated that the “ring” or “annulus” portions are used herein todescribe the general shape of the plurality of concentric ring (orannulus) portions 111 to 116. The “ring” or “annulus” portions mayinclude discontinuities.

In an example, thicknesses of the ring portions may be in a range from0.18 um to 2.5 um and the two adjacent ring portions may be spaced outby a distance in a range from 0.22 um to 3 um. A thickness of arespective ring portion is defined herein as the minimum distancebetween the inner perimeter and the outer perimeter of the ring portion,for example, the thickness of the ring portion 114 is denoted as “t” asshown in FIGS. 1A and 1B. A distance of the two consecutively adjacentring portions including an inner ring portion and an outer ring portionis defined herein as the minimum distance between the inner perimeter ofthe outer ring portion and the outer perimeter of the inner ringportion, for example, the distance of the ring portion 115 is denoted as“d” as shown in FIG. 1B. A thickness of the ring portion 111 may besmaller than a thickness of the ring portion 112, the thickness of thering portion 112 may be smaller than a thickness of the ring portion113, the thickness of the ring portion 113 may be smaller than athickness of the ring portion 114, the thickness of the ring portion 114may be smaller than a thickness of the ring portion 115, and thethickness of the ring portion 115 may be smaller than a thickness of thering portion 116.

The first region 110 may further include a plurality of substrateportions in between the plurality of concentric ring portions 111 to116. A thickness of the substrate portion in between the ring portion111 and the ring portion 112 may be smaller than or equal to a thicknessof the substrate portion in between the ring portion 112 and the ringportion 113, and so forth. While six concentric ring portions have beenpresented herein, it should be appreciated that the number of concentricring portions may be more or less than six, and the exemplary number ofsix is not intended to limit the scope, applicability or configurationof the claimed subject matter in any way.

The plurality of the concentric ring portions 111 to 116 may besubstantially located concentric with the first ring region 120 and thesecond ring region 140. It should be appreciated that being concentricprovides direct and quick current paths between the ring regions;however, the ring regions may not be concentric and instead eccentricwith an inner ring region being at least partially enclosed by an outerring region.

As will be discussed further herein, the first region 110 including theplurality of concentric ring portions 111-116 may be further annealed toprovide a gradual graded doping. The concentric ring portions 111 to 116may not be clearly defined after annealing which may depend on adistance between the adjacent ring portions and/or a thickness of thering portion. The concentric ring portions 111 to 116 illustrated inFIGS. 1A-1B illustrate an example of a possible arrangement of theplurality of concentric ring portions 111-116 prior to annealingrelative to the first ring region 120.

In an example, the first ring region 120 may include a continuousguardring portion 120 a as shown in FIG. 1A and in another example, thefirst ring region 120 may include a digitated discontinuous guardringportion 120 b as shown in FIG. 1B. The device 100 a may include thefeatures of the device 100 b except for the feature 120 a whereas thedevice 100 b has the different feature 120 b as discussed herein. Thedigitated discontinuous guardring portion 120 b may include a pluralityof guardring portions spaced apart by a plurality of gap portions. Theplurality of guardring portions may include multiple guardring portionshaving a same length (denoted as “S_(w)”) and the multiple guardringportions having the same length may be arranged in two parallel lines.One of the multiple guardring portions in one of the parallel lines maybe in alignment with another multiple guardring portion in the other ofthe parallel lines. The plurality of guardring portions may also includetwo half ring portions arranged at each end of the two parallel lines.The plurality of gap portions may have a same length (denoted as“S_(s)”) that is smaller than or equal to the length S_(w) of theplurality of guardring portions. Greater details will be discussedbelow.

The device 100 may further include a first isolation region 160 disposedin the first region 110. The first isolation region 160 may be ringshaped. The isolation regions discussed herein may be shallow trenchisolation (STI) or local oxidation of silicon (LOCOS) regions and have across-section of a trapezoid or a hexagonal prism. An inner edge of thefirst isolation region 160 may be in direct contact with the first ringregion 120, and an outer edge end of the first isolation region 160 maybe in direct contact with the second terminal region 140 and the secondring region 150. The inner edge of the first isolation region 160 may bespaced apart with the first terminal region 130 so as to reduce leakageunder the off state.

Referring to FIG. 2 , the first isolation region 160, in across-sectional view, may include a first portion 161 and a secondportion 162 of the first isolation region 160. The first portion 161 ofthe first isolation region 160 extends between the first portion 131 ofthe first terminal region 130 and the first portion 151 of the secondterminal region 150, and the second portion 162 of the first isolationregion 160 extends between the second portion 132 of the first terminalregion 130 and the second portion 152 of the second terminal region 150.

The device 100 may further include a first field poly plate 170 disposedover the first isolation region 160. The first field poly plate 170 maybe ring shaped. The first field poly plate 170 may be connected to theanode 101 and disconnected with the first and second terminal regions130, 150. The first field poly plate 170, in a cross-sectional view, mayinclude a first portion 171 and a second portion 172 of the first fieldpoly plate 170. The first portion 171 of the first field poly plate 170is disposed over the first portion 161 of the first isolation region 160and the second portion 172 of the first field poly plate 170 is disposedover the second portion 162 of the first isolation region 160.

The first, second terminal regions 130, 150 may include ring regionsconcentric with the first, second ring regions 120, 140. The firstisolation region 160, the first field poly plate 170 may also includering regions concentric with the first, second ring regions 120, 140.

The device 100 may further include a second isolation region 180 atleast partially disposed in the first region 110. The second isolationregion 180 may be ring shaped. The second isolation region 180 mayextend laterally from the second ring region 140, a first end of thesecond isolation region 180 being in direct contact with the secondterminal region 150 and the second region 140. In alternativeembodiments, the first end of the second isolation region 180 may bespaced apart from the second terminal region 150 and the second region140. The device 100 may further include a deep isolation region 190 indirect contact with the second isolation region 180 and extending to theburied oxide layer 109. The second isolation region 180, in across-sectional view, may include a first portion 181 and a secondportion 182 of the second isolation region 180. The second isolationregion 180 and the deep isolation region 190 may include a square regionenclosing the first region 110, the first ring region 120 and the secondring region 140, thereby no leakage path through the substrate 108. Thedeep isolation region 190, in a cross-sectional view, may include afirst portion 191 and a second portion 192 of the deep isolation region190, with the first portion 191 in direct contact with the first portion181 of the second isolation region 180 and the second portion 192 indirect contact with the second portion 182 of the second isolationregion 180. The second isolation region 180 may be integrated with thedeep isolation region 190 and have the same material composition.

The device 100 may further include a silicide layer 103 disposed overthe first terminal region 130, the first ring region 120 and the firstregion 110, wherein the first terminal region 120 is connected to theanode 101 through the silicide layer 103. The silicide layer may helpguide current flow to the anode 101.

In various non-limiting embodiments, the substrate 108 may include anysilicon-containing substrate including, but not limited to, silicon(Si), single crystal silicon, polycrystalline Si, amorphous Si,Epitaxial (EPI) Si, silicon-on-sapphire (SOS), silicon-on-insulator(SOI) or silicon-on-replacement insulator (SRI) or silicon germaniumsubstrates and the like. The substrate 108 may in addition or insteadinclude various isolations, dopings and/or device features. Thesubstrate 108 may include other suitable elementary semiconductors, suchas, for example, germanium (Ge) in crystal, a compound semiconductor,such as silicon carbide (SiC), gallium arsenide (GaAs), galliumphosphide (GaP), indium phosphide (InP), indium arsenide (InAs), galliumnitride (GaN), aluminium nitride (AlN), indium nitride (InN), and/orindium antimonide (InSb) or combinations thereof; an alloy semiconductorincluding GaAsP, AlInAs, GaInAs, GaInP, AlGaN, or GaInAsP, orcombinations thereof.

FIG. 3 shows a partial equivalent circuit of the device 100. Gradeddoping concentration of the first region 110 provides a lower resistanceR from the cathode 102 to the anode 101 and accordingly lower forwardingvoltages and higher reverse breakdown voltages of the device 100.Furthermore, the buried oxide layer 109 disconnects the collectorsubstrate 108 and therefore prevents a parasitic bipolar junctiontransistor (BJT) formed by the first terminal region 130, the first ringregion 120, the first region 110 and the substrate 108. Additionally,double reduced-surface-field effect (RESURF) from the field poly plate170 and the buried oxide layer 109 promotes higher reverse breakdownvoltages.

FIG. 4 shows simulated total current densities for the device 100 intechnology computer aided design (TCAD). The intensive contours of totalcurrent density are present from the cathode 102 to the anode 101, withstronger currents 401 located at lower doping concentration ringportions of the first region 110 and weaker currents 402 located athigher doping concentration ring portions. RESURF can also been seenfrom FIG. 4 .

FIG. 5 shows a cross section view of the device 100 along the B-B′ lineof FIG. 1(B) according to various embodiments of the present disclosure.The B-B′ line comes across the gap portions of the first ring region 120and accordingly, the first ring region 120 including the guardringportion is absent in FIG. 5 .

FIG. 6A shows the forwarding voltages of the device 100 of FIG. 1A andFIG. 6B shows the breakdown voltages of the device 100 of FIG. 1A, whenthe anode length (denoted as “L” in FIG. 1A and FIG. 2 ) is 0.5 um, 1 umand 2 um. As it can be seen from Graph 601 and Graph 602 when the anodelength is 0.5 um, the forwarding voltage is 0.64 V as the current is 0.1uA and 0.70 V as the current is 1 uA, and the breakdown voltage is 86 V.As the anode length increases to 1 um and as seen from Graph 603 andGraph 604, the forwarding voltage is 0.4 V as the current is 0.1 uA and0.53 V as the current is 1 uA, and the breakdown voltage is 54 V. As theanode length further increases to 2 um and as seen from Graph 605 andGraph 606, the forwarding voltage is 0.33 V as the current is 0.1 uA and0.44 V as the current is 1 uA, and the breakdown voltage is 54 V.Accordingly, both the forwarding voltage and the breakdown voltagedecrease as the anode length increases from 0.5 um to 2 um. Therefore, asuitable and optimum value of the anode length can be achieved from thepresent disclosure.

FIG. 7A shows the forwarding voltages of the device 100 of FIG. 1B whenthe anode length is 1.0 um and 1.4 um, and the length S_(s) of pluralityof gap portions is 1um and equal to the length S_(w) of the plurality ofguardring portions of the first ring region 120 b. FIG. 7B shows thebreakdown voltages of the device 100 of FIG. 1B when the anode length is1 um and 1.4 um, and S_(s) is 1.4 um, smaller than S_(w) which is 1.8um. As it can be seen from Graph 701 and Graph 702 when the anodelength, S_(s) and S_(w) are at 1 um, the forwarding voltage is 0.34 V asthe current is 0.1 uA and 0.40 V as the current is 1 uA, and thebreakdown voltage is 78 V. As the anode length and S_(s) increase to 1.4um and S_(w) increases to 1.8 um, Graph 703 shows that the forwardingvoltage is 0.35 V as the current is 0.1 uA and 0.42 V as the current is1 uA, and Graph 704 shows that the breakdown voltage is 50 V.Accordingly, the forwarding voltage does not change significantly andthe breakdown voltage increases as the anode length and S_(s) decreasesfrom 1.4 um to 1.0 um and S_(w) decreases from 1.8 um to 1 um.Therefore, the anode length, S_(s), S_(w) can be varied to achieveoptimum forwarding voltages and breakdown voltages from the presentdisclosure.

FIGS. 8A to 8D show simplified cross-sectional views that illustrate amethod 800 for fabricating the device 100 according to variousnon-limiting embodiments. Referring to FIG. 8A, the method 800 mayinclude providing a buried oxide layer 109 on a substrate 108 andproviding a first region 110 on the buried oxide layer 109. Providingthe first region 110 may include using a photoresist mask 810 whendoping the first region 110 as shown in FIG. 8A and annealing the firstregion 110 after doping the first region 110 to allow the activation anddiffusion of dopants as shown in FIG. 8B. For example, the photoresistmask 810 may have a pattern including a plurality of concentric ringpatterns 811, 812, 813, 814 for providing a plurality of concentric ringportions 111, 112, 113, 114 in the first region 110, and the sizes ofthe ring patterns may increase in a radial direction from the centerconcentric ring patterns 811, 812, to the perimeter concentric ringpattern 814 corresponding to the thicknesses of the plurality ofconcentric ring portions 111, 112, 113, 114. It shall be appreciatedthat the number of the concentric rings shown is just for illustrationand provides those skilled in the art with a convenient road map forfabricating the devices. For example, the center ring portion 111 of thefirst region 110 may be formed by doping the region in between theconcentric ring patterns 811, 812. During doping the first region 110,the doping material is directed into the specific areas 820 where nopatterns of the plurality of concentric ring patterns 811 to 814 exist,as shown by the arrows in 820. The plurality of the concentric ringpatterns 811 to 814 may have sizes in a range from 0.22 um to 3 um andbe spaced out by distances in a range of 0.18 um to 2.5 um.

As shown in FIG. 8C, the method 800 may further include providing afirst isolation region 160 and a second isolation 180 disposed in thefirst region 110, and providing a deep isolation region 190 being indirect contact with the buried oxide layer 109. As shown in FIG. 8D, themethod 800 may further include providing a first ring region 120 and asecond ring region 140 in the first region 110, providing a firstterminal region 130 disposed in the first ring region 120 and a secondterminal region 150 disposed in the second ring region 140, andproviding a first field poly plate 170. The first terminal region 130may be connected to the anode 101 and the second terminal region 150connected to the cathode 102.

Now referring to FIG. 9 , a device 200 is presented according to othervarious non-limiting embodiments. The device 200 may include thefeatures of the device 100 as described above in connection to FIG. 2 ,and therefore, the common features are labelled with the same referencenumerals and need not be discussed. The device 200 may further include aLaterally Diffused N-type Metal Oxide Semiconductor (LDNMOS) region 200a, which includes a second region 210, and a third region 220 disposedin the second region 210, the third region 220 being connected to adrain 201 and in direct contact with the buried oxide layer 109. Thesecond region 210 may be a draft region and the third region 220 may bea middle voltage well region.

The LDNMOS region 200 a may further include a third ring region 230disposed at least partially in the second region 210 and the third ringregion 230 may be connected to a source 202 and in direct contact withthe buried oxide layer 109. The third ring region 230 may be a middlevoltage well region. The LDNMOS region 200 a may also include a thirdisolation region 240 disposed in the second region 210 extending betweenthe third region 220 and the third ring region 230. The third isolationregion 240 may be in direct contact with the third region 220. A secondend of the second isolation region 180 may be in direct contact with thethird ring region 230, and the deep isolation region 190 may be locatedbetween the second ring region 140 and the third ring region 230. Thesecond region 210 and the third region 220 may have a first conductivitytype and the third ring region 230 may have a second conductivity type.The ring regions in the LDNMOS region 200 a may be concentric with thering regions of the device 100 that is the Schottky diode region.Alternatively, the ring regions in the LDNMOS region 200 a may beconcentric with the ring regions of the device 100 in accordance withoperation voltage ratings.

The LDNMOS region 200 a may further include a second field poly plate250 disposed over the third isolation region 240, the second region 210and the third ring region 230. The LDNMOS region 200 a may also includea fourth isolation region 260 expanding from the third ring region 230and an additional deep isolation region 270 in direct contact with thefourth isolation region 260 and the buried oxide layer 109.

FIGS. 10A to 10D show simplified cross-sectional views that illustrate amethod 900 for fabricating the device 200 according to variousnon-limiting embodiments. The method 900 may include the steps of themethod 800 as described above in connection to FIGS. 8A to 8D. Referringto FIG. 10A, the method 900 may include providing a buried oxide layer109 on a substrate 108 and providing a first region 110 on the buriedoxide layer 109. The method may also include providing a second region210 on the buried oxide layer 109. Providing the first region 110 mayinclude using a photoresist mask 910 when doping the first region 110and the second region 210 as shown in FIG. 10A and annealing afterdoping as shown in FIG. 10B. The photoresist mask 910 may have a patternincluding a plurality of concentric ring patterns 911 to 914 configuredto provide the plurality of concentric ring portions 111 to 114, and thesizes of the ring patterns may increase in a radial direction from thecenter ring patterns 911, 912 to the perimeter ring pattern 914, in asimilar manner as the photoresist mask 810. The photoresist mask 910 mayfurther include an opening 919 where the second region 210 is depositedwith doping materials.

As shown in FIG. 10C, the method 900 may further include providing afirst isolation region 160 and a second isolation 180 disposed in thefirst region 110, and providing a deep isolation region 190 being indirect contact with the buried oxide layer 109. The method 900 may alsoinclude providing a third isolation region 240, a fourth isolationregion 260 and an additional deep isolation region 270.

As shown in FIG. 10D, the method 900 may further include providing afirst ring region 120 and a second ring region 140 in the first region110, providing a first terminal region 130 disposed in the first ringregion 120 and a second terminal region 150 disposed in the second ringregion 140, and providing a first field poly plate 170. The firstterminal region 130 may be connected to the anode 101 and the secondterminal region 150 connected to the cathode 102. The method 900 mayalso include providing a second region 210, a third region 220, a thirdring region 230 and a second field poly plate 250. The third region 220may be connected to a drain 201 and the third ring region 230 may beconnected to a source 202.

The above described order for the method is only intended to beillustrative, and the method is not limited to the above specificallydescribed order unless otherwise specifically stated.

In various non-limiting embodiments, the devices 100, 200 may beconventionally fabricated, for example, using known processes andtechniques (e.g., growing epitaxial material and implanting impurities).For example, the p-type material may be or include, but is not limitedto boron doped silicon as a material, and/or the n-type material may beor include, but is not limited to doped silicon material includingphosphorus dopants, arsenic dopants, or combinations thereof.

FIG. 11 shows the doping concentration and electrical fieldcharacteristics of the first region 110. Graph 1101 depicts a decreasingdoping concentration across the first region 110 from the cathode sideto the anode side. Graph 1102 depicts substantially uniform electricalfield 1102 across the first region 110 from the cathode side to theanode side.

Various modifications can be made to the device 100 as described herein.Similar modifications as those described with reference to device 100may be made to devices 200.

For example, the distances between the ring portions 111 to 116 of thefirst region 110 as shown in FIGS. 1A and 1B may be varied. By varyingthese distances, the lateral graded junction in the first region 110 isvaried and therefore the breakdown voltages of the device 100 can beadjusted to a desired level. In an example, the distance between any tworing portions of the first region 110 may be zero, that is, the two ringportions are in direct contact with each other. In an example, twoadjacent ring portions may be overlapped, that is, there is no visibleboundary between the two adjacent ring portions of the first region 110.The variation of the distances varies the breakdown voltages withgreater distance between two ring portions resulting in higher breakdownvoltage. By reducing the distance between two ring portions, thebreakdown voltages can be reduced. The device 100 provides scalablebreakdown voltages for high voltage applications.

Further, the thicknesses of the ring portions of the first region 110may be varied, and the electrical characteristics and performance of thedevice 100 may be varied accordingly. The difference between thethicknesses of two adjacent ring portions can be also varied, wherebythe graded doping concentration of the first region 110 may be varied.

In FIG. 2 and the description set forth, the first region 110, thesecond ring region 140, the second terminal region 150 are indicated asn-doped conductivity; and the substrate 108, the first ring region 120and the first terminal region 130 are indicated as p-doped conductivity.It can be understood by a person skilled in the art that the firstregion 110, the second ring region 140, the second terminal region 150can have a different conductivity or an opposite conductivity, e.g.p-doped conductivity; and that the substrate 108, the first ring region120 and the first terminal region 130 can have a different conductivity,e.g. n-doped conductivity. Furthermore, in FIG. 9 , the second region210 and the third region 220 are shown as n-doped conductivity region,and it can be understood that they can be a different conductivity asdiscussed herein. Similarly, the third ring region 230 is shown asp-doped conductivity region, and it can be understood that it can be adifferent conductivity as discussed herein. The device 100 may also bemodified such that only some regions are replaced with respectiveregions of an opposite conductivity type. For instance, the substrate108 can be replaced with an n-type substrate, while the conductivitytype of the rest of the device 100 remains the same. It would be clearto a person skilled in the art that the directions of current flows willchange accordingly when the conductivity types of the various regionsare reversed.

In various non-limiting embodiments, the first terminal region 130 andthe second terminal region 150, may include one or more dopants orcombinations thereof and may have the same doping concentrations (i.e.same concentration of dopants) or different doping concentrations (i.e.different concentrations of dopants) from each other. The highest dopingconcentration of the graded doping concentration of the first region 110may be lower than the doping concentration of the second ring region140. That is, the doping concentration of the second ring region 140 ishigher than the highest doping concentration of the graded dopingconcentration of the first region 110.

The doping levels of the various regions may be varied, the electricalcharacteristics and performance of the devices 100, 200 as describedherein will be varied accordingly.

Furthermore, the positioning of the regions of the device 100 may bevaried and one region may be partially or fully within another region.For instance, the second ring region 140 may be partially or fullywithin the first region 110.

The isolation regions 160, 180, 190, may be positioned differently. Thecross-sectional view of the isolation regions 160, 180, 190, may be anyshape other than trapezoid. The sizes of the isolation regions 160, 180,190, may be adjusted to be less or larger in the lateral direction or inthe vertical direction.

In addition, the surfaces of the devices 100, 200, are not intended tolimit to flat surfaces. In various non-limiting embodiments, thesurfaces of the devices 100, 200, can be curved surfaces.

The disclosure may be embodied in other specific forms without departingfrom the spirit or essential characteristics thereof. The foregoingembodiments, therefore, are to be considered in all respectsillustrative rather than limiting the disclosure described herein. Scopeof the disclosure is thus indicated by the appended claims, rather thanby the foregoing description, and all changes that come within themeaning and range of equivalency of the claims are intended to beembraced therein.

1. A device comprising: a buried oxide layer disposed on a substrate; afirst region disposed on the buried oxide layer; a first ring regiondisposed in the first region, the first ring region comprising a portionof a guardring; a first terminal region disposed in the first ringregion, the first terminal region being connected to an anode; a secondring region disposed in the first region; a second terminal regiondisposed in the second ring region, the second terminal region beingconnected to a cathode; wherein the first region has a graded dopingconcentration; wherein the first region, the second ring region, and thesecond terminal region have a first conductivity type; wherein the firstring region and the first terminal region have a second conductivitytype; and wherein the first conductivity type is different from thesecond conductivity type.
 2. The device according to claim 1, whereinthe first region has a rounded shape and wherein the dopingconcentration of the first region increases in a radial direction from acenter of the first region to a perimeter of the first region.
 3. Thedevice according to claim 1, wherein the first region comprises aplurality of concentric ring portions, and wherein the dopingconcentration of the first region increases in a radial direction from acenter ring portion to a perimeter ring portion.
 4. The device accordingto claim 3, wherein the plurality of the concentric ring portions islocated concentric with the first ring region and the second ringregion.
 5. The device according to claim 3, wherein the first regionfurther comprises a plurality of substrate portions in between theplurality of concentric ring portions.
 6. The device according to claim1, further comprises: a first isolation region disposed in the firstregion, an inner edge of the first isolation region being in directcontact with the first ring region, an outer edge end of the firstisolation region being in contact with the second terminal region andthe second ring region.
 7. The device according to claim 6, furthercomprising: a first field poly plate disposed over the first isolationregion, the first field poly plate being connected to the anode.
 8. Thedevice according to claim 7, wherein the first field poly plate isdisconnected with the first and second terminal regions.
 9. The deviceaccording to claim 1, wherein the first ring region comprises adiscontinuous guardring portion.
 10. The device according to claim 9,wherein the discontinuous guardring portion comprises a plurality ofguardring portions spaced apart by a plurality of gap portions.
 11. Thedevice according to claim 10, wherein the plurality of guardringportions has a length larger than a length of the plurality of gapportions.
 12. The device according to claim 1, further comprising: asecond isolation region at least partially disposed in the first region,the second isolation region extends laterally from the second ringregion, a first end of the second isolation region being in directcontact with the second terminal region and the second region; and adeep isolation region in direct contact with the second isolation regionand extending to the buried oxide layer.
 13. The device according toclaim 1, further comprising a silicide layer disposed over the firstterminal region, the first ring region and the first region, wherein thefirst terminal region is connected to the anode through the silicidelayer.
 14. The device according to claim 12, wherein the device furthercomprises: a second region; a third region disposed in the secondregion, the third region being connected to a drain and in directcontact with the buried oxide layer; a third ring region disposed in thesecond region, the third ring region being connected to a source and indirect contact with the buried oxide layer; and a third isolation regiondisposed in the second region extending between the third region and thethird ring region, the third isolation region being in direct contactwith the third region, wherein a second end of the second isolationregion is in direct contact with the third ring region; wherein the deepisolation region is located between the second ring region and the thirdring region; wherein the second region and the third region have a firstconductivity type; and wherein the third ring region has a secondconductivity type.
 15. The device according to claim 14, furthercomprising a second field poly plate disposed over the third isolationregion, the second region and the third ring region.
 16. The deviceaccording to claim 1, wherein the first, second terminal regionscomprise a first, second terminal ring regions.
 17. The device accordingto claim 1, wherein a doping concentration of the second ring region islower than a doping concentration of the first region.
 18. The deviceaccording to claim 1, wherein the first region is a drift region.
 19. Amethod for manufacturing a device, comprising: providing a buried oxidelayer on a substrate; providing a first region on the buried oxidelayer; providing a first ring region and a second ring region in thefirst region; and providing a first terminal region disposed in thefirst ring region and a second terminal region in the second ringregion, the first terminal region being connected to an anode and thesecond terminal region being connected to a cathode, wherein providingthe first region comprises: using a photoresist mask when doping thefirst region; and annealing the first region after doping the firstregion; wherein the photoresist mask has a plurality of concentricrings; and wherein the first region, the second ring region, and thesecond terminal region have a first conductivity type; wherein the firstring region and the first terminal region have a second conductivitytype; and wherein the first conductivity type is different from thesecond conductivity type.
 20. The method of claim 19, wherein sizes ofthe plurality of concentric rings increase in a radial direction awayfrom a centre.